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How to Set Your Heart Rate Zones

Your physiology is beautifully unique. I sound like John Mayer if he was a physical therapist. Our bodies are wonderlands, even if our glutes are unmaintained landfills.

The individual uniqueness of athletes creates a problem, though. How can we understand our physiology in the broader context of training theory when every variable is a bell curve across the population? General equations work if you're smack-dab in the middle of the bell curve thiccness, but can be actively wrong and counterproductive as you venture into the standard deviation hinterlands.

Consider the equation that many of you might have heard about heart rate: 180 beats per minute minus age = approximately aerobic threshold, or the intensity level that serves as a top-end barrier for easy/steady running that should encompass around 80% of your training volume. While that equation is generally useful, it can be actively useless for individuals, especially aging athletes who are highly trained and have a much higher aerobic threshold than the equation would predict.

For me, the equation caps my easy runs at 145 heart rate. My actual aerobic threshold is 152 beats per minute in running (and 150 beats per minute in biking). In practice, that's almost a one-minute-per-mile difference in output. Training from a general equation would prevent me from accruing benefits from steadier paces, and I'd probably be slower at everything.

raining zones from your watch can also be atrocious. In the last few months, I have helped a few hundred listeners of our podcast calculate their heart rate zones (our episode on heart rate zones is here). And a lesson I learned is that some of the watch brands use algorithms that are less accurate than U2 in Spanish class. Zone Uno, Zone Dos, Zone Tres, Zone Catorce, Zone Biblioteca, etc. Some of the watch zones are set so low that I have no idea what they could possibly be measuring. 

So today, let's look at one simple way to calculate your heart rate zones to help you calibrate your training intensity. Knowing your intensity ranges is helpful because it optimizes your metabolic fitness, allowing the body to burn more fat at higher outputs, while supporting mitochondrial proliferation and efficiency, allowing both higher and lower intensities to take less energy. Disclaimer: exercise physiology terminology is always subject to evolving debate, particularly on Twitter (the world's town square, if the square was also where the town put the raw sewage). Here is my favorite infographic ever on the overlap of these principles, from Fluid Athletics (follow them on Instagram here). 

What Are Heart Rate Zones?

We'll be using the traditional Five-Zone model, contrasted with the Three-Zone model used in most training research, but it helps to understand both and how they interact. Heart rate is best thought of as a proxy for lactate concentrations. To simplify it a ton, lactate is produced as our bodies use glucose to fuel ATP production during glycolysis. Lactate is a fuel source for cells, and it's accompanied by a hydrogen ion that changes muscle pH and contributes to fatigue. A 2018 review in Cell Metabolism described the lactate shuttle where the cells use lactate for energy. If this shuttling mechanism is overstressed, lactate levels and fatigue rise and exercise becomes less sustainable. A great overview by Dr. Howard Luks is here.

When lactate concentrations begin to rise, intensity switches from easy to moderate, an inflection point known as LT1, broadly overlapping with aerobic threshold where athletes go from primarily burning fat to primarily burning glycogen. And when lactate levels rise more steeply at higher intensities, intensity transitions from moderate to hard, an inflection point known as LT2, broadly overlapping with traditional lactate threshold (or critical velocity, depending on the method of calculation). That encompasses the 3-Zone model used in research:

Those zones are used in research to determine intensity distribution. While these breakdowns are gross approximations, it can help to put some numbers on paper to get your bearings (all of these numbers have big error bars). 

So if we're using heart rate to approximate lactate and the associated physiological impacts of fatigue, why don't we just use lactate? Good question, you article-ruining jerk. In a perfect world, athletes may decide to prick themselves for blood lactate readings with every interval like they're Norwegian vampires. Practically, though, there's a lactate learning curve in the best of times that can lead to inaccurate data, and in the worst of times it can take some of the spontaneous artistry out of daily training. You can probably tell I'm scared of blood, needles, and vampires (whether traditional or sexy). 

But have blood-free hope! Using the method in the article, I have approximated zones for professional athletes that have later been validated in lab tests with small enough margins of error to be useful. However, it's key to get a full lab test for truly accurate data. Heart rate without lactate, metabolic, and/or ventilatory lab tests is like determining the time from where the sun is in the sky. With context clues, you can be close, but you wouldn't want to use it to cook a turkey.

Five-Zone Training Model

Now, let's finally get to the Five-Zone heart rate model that is used in most training approaches. The Three-Zone model is overlaid with green, yellow, and red (again, there is debate around the exact breakdown, particularly with the Zone three/Zone four delineation).

There are a few ways to set the zones, but I see the most repeatability and accuracy with the Lactate Threshold Heart Rate method pioneered by legendary coach Joe Friel. As outlined in Training Peaks, he suggests that athletes "do a 30-minute time trial all by yourself (no training partners and not in a race). Again, it should be done as if it was a race for the entire 30 minutes. But at 10 minutes into the test, click the lap button on your heart rate monitor. When done, look to see what your average heart rate was for the last 20 minutes." 

I like athletes to do the test on uphills, where they won't be limited by neuromuscular and biomechanical factors if they don't have a ton of speed training. If it wasn't a truly hard effort or your heart rate takes a lot of time to increase across an effort, you can take the average heart rate from a section as short as 10 minutes. Because this isn't an exact measurement like in a lab test, think of it as an art that is useful in understanding your body, rather than attempting to find a correct answer like high school algebra.

For an easy way to scrub complex data files with HR variation, you can use the Strava Sauce browser plug-in, highlight the area you want to examine, and it will give averages without ever lapping the watch. When I calculate zones for athletes, I have found that you can also approximate LTHR from almost any hard workout with intervals 3 minutes or over by looking for spots in the file where heart rate stabilizes for 15-30 seconds before rising to less sustainable levels (and sometimes falling back toward that baseline in longer efforts). Be careful about using data from very hot days or long races over 90 minutes, when heart rate can sometimes be sustained above Friel's LTHR in ways that are not mirrored by the underlying physiology. 

A big key here: the data needs to be accurate. Chest-straps are ideal for these purposes, and if you are doing a workout to set heart rate zones, it's worth using the chest strap even if it feels like you're getting the heimlich maneuver from a weak octopus. While wrist-straps are rapidly improving in accuracy, there is extreme variation among athletes/watch brands. For example, my Garmin 745 seems to work really well in most circumstances (see this beautiful graph of a threshold workout). But other athletes don't have that success, and sometimes they send me heart rate files that look like Bitcoin price graphs (we are not sure why it's going up and down, but we can be pretty sure it's nefarious). 

How to Set Your Heart Rate Zones

Once you have the LTHR number, it's time to set those elusive zones. We're at another controversial point where the exact percentages are subject to extreme debate. The problem: when you validate heart rate data with lab tests, individual physiology varies substantially. LTHR narrows down that physiological variation to get an idea of zones, but the exact delineation depends on training history, muscle fiber typology, metabolic context, astrological sign, etc. Don't even get me started on Scorpios.

Here are the percentages that Megan and I like to use:

Let's dig into an example from my data. In February, I did a virtual bike race up a mountain. Using the Strava Sauce plug-in and highlighting the final 20 minutes of that hard effort, my LTHR was 172. While there is variance across sports and my heart rate is higher with running, that means my current zones for biking are approximately:

Your LTHR may increase with training and it will drop with age. Athletes are often between 165 and 175, though in professional athletes, I have seen numbers as high as 189 and as low as 152. You can see why dialing in your unique physiology is so important. An athlete with an LTHR of 160 needs to cap most of their easy runs at 140 heart rate (top end of Zone 2). Meanwhile, an athlete with an LTHR of 180 can go all the way up to 157! Often, everything about those athletes can look the same from the outside-same age, same PRs, same training, same potential. But they have very different hearts.

How To Use Your Heart Rate Zones

There are two places where having a general feel for your personal heart rate zones can be most helpful: understanding your Zone 2 (with LT1 as a cap) and determining the sustainability of longer efforts. First, let's break down how to think about each of the zones:

Knowing that Zone two cutoff can help calibrate an athlete's effort so they understand what terms like "easy," "steady," and "moderate" actually mean. Spot-checking heart rate periodically on harder efforts can ensure that athletes aren't going too hard, pushing everything into Zone five and reducing aerobic adaptations. I love athletes to get a feel for how high their heart rate gets on uphills especially, since excessive effort on ups can lead to reduced endurance and race performance. Zone 3 is your friend, in moderation. Zone four is your acquaintance. And spending too much time with Zone five will end with you folded up in a car trunk somewhere outside Las Vegas.

Takeaway

The big takeaway is that heart rate is just a proxy for fatigue processes, especially when calculated outside of a lab. The numbers can vary by the day, and they change across training blocks. Temperature, stress, caffeine, and political news all impact the numbers enough that caring too much about a few beats per minute is unhelpful. The day I first heard the nickname "Meatball Ron," I was in Zone three while sitting on the couch.

Instead, view heart rate as a way to calibrate your physiology in a general way, spot-checking your perceived exertion so that you know what you think your body is doing generally aligns with what your body is actually doing. Once an athlete dials in heart rate, I like them to look at it once every couple weeks during a run, and solely after-the-fact on other runs (if at all), never investing too much in small changes. Heart rate sometimes takes a while to respond, so I find it's rarely useful on shorter intervals.

If you train within the correct general range of intensities, whether guided by heart rate, lactate, and/or perceived exertion, you can improve output at Zone two and Zone three heart rates in particular, and because those efforts are more sustainable metabolically, you'll excel in races. You definitely don't need to have a heart rate monitor to achieve those goals. But you do need to have a good feel for your unique physiology. 

All of our bodies can be well-calibrated wonderlands. We sometimes just need a little bit of the sexiest thing of all: data.

(04/22/2023) Views: 3,307 ⚡AMP
by Trail Runner Magazine